1. Field of the Invention
The present disclosure relates to systems and methods for registering anatomical image data sets and relating anatomical information between anatomical image data sets.
2. Description of the Background of the Invention
There exist various techniques in computer assisted surgical procedures to register patient related data across different modalities and/or different time frames. Such patient related data can include, for example, anatomical information or image data obtained using a variety of imaging techniques or modalities, such as ultrasound, magnetic resonance imaging (“MRI”), computed tomography (“CT”), single photon emission computed tomography, positron emission tomography, etc. One technique to register patient related data across different modalities is a “point to point” or “paired point” matching technique, wherein landmarks or fiducials that can be identified across different modalities are used to determine a transformation matrix and establish a spatial relationship between the different modalities. In one example, landmarks or fiducials are placed on a patient prior to an image scan, for example, an MRI or CT scan, and such landmarks or fiducials are identified in the image scan and on the patient during a surgical procedure to establish the registration between the patient and patient related data from the image scan.
In another technique, surface registration is used, wherein multiple surface points of a structure or region of interest are used to establish a registration surface. The surface points are identified independently in different modalities often using different techniques. In one embodiment, the surface registration technique is used in ear-nose-throat surgery where a face of a patient is used as a registration surface. For example, a CT or MRI scan of the face of the patient is obtained and the surface of the skin is identified in the scan and then matched to digitized points on the face of the patient during surgery. Such digitized points can either be collected directly with a digitization device, such as a pointer, or indirectly via a registration mask.
The above registration techniques generally serve only to register patient related data from one modality to a different modality. Most commonly, the registration techniques register pre-operative image data of a patient to the anatomy of the patient during surgery for localization purposes of surgical instruments used to perform the surgery.
In some types of procedures, such as procedures related to musculo-skeletal ailments, biomechanical and functional information of joints play an important role in determining the extent or cause of a disease. Such information is generally captured through a motion analysis. In one example of a motion analysis, fiducials are placed on the skin of a body part to be analyzed. A navigation system tracks the fiducials as the body part is moved and the movement of the fiducials is analyzed to establish a biomechanical model of the body part. An obvious downside of this technology is that the fiducials do not directly relate to the underlying bony structures and that shifts in skin or soft tissue occurs during motion. Such shifts can contribute to relatively large motion artifacts and inaccuracies in the results of the motion analysis and the established biomechanical model.
A technique that overcomes soft tissue shift is the direct implantation of fiducials, such as small tantalum beads, onto the bones of the subject, wherein the fiducials are tracked using stereo-radiography techniques during movement of the body part of the patient. Some of the obvious disadvantages of this technique are that a surgical procedure is required for bead implantation and that the motion analysis utilizes ionizing energy.
Further, during a surgical procedure, a motion analysis may not adequately capture functional information of the joints if the motion of the limb is passive. For example, when a surgeon moves the limbs of a patient, or if the patient is anesthetized and lying on an operating room table, no voluntary muscular forces are active to counter the effects of gravity on the body masses.
As surgical procedures around musculo-skeletal ailments start to shift away from pure static standing considerations to a more functional assessment of the joints and towards early intervention, the ability to capture joint related functional information and easily relate such information to the planning and execution of surgical procedures becomes increasingly important.